Thinking, Fast and Slow

Two Systems
Psychologists have been intensely interested for several decades in the
two modagee fi Pn="cees of thinking evoked by the picture of the angry
woman and by the multiplication problem, and have offered many labels for
them. I adopt terms originally proposed by the psychologists Keith
Stanovich and Richard West, and will refer to two systems in the mind,
System 1 and System 2.
System 1
operates automatically and quickly, with little or no effort
and no sense of voluntary control.
System 2
allocates attention to the effortful mental activities that
demand it, including complex computations. The operations of
System 2 are often associated with the subjective experience of
agency, choice, and concentration.
The labels of System 1 and System 2 are widely used in psychology, but I
go further than most in this book, which you can read as a psychodrama
with two characters.
When we think of ourselves, we identify with System 2, the conscious,

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reasoning self that has beliefs, makes choices, and decides what to think
about and what to do. Although System 2 believes itself to be where the
action is, the automatic System 1 is the hero of the book. I describe
System 1 as effortlessly originating impressions and feelings that are the
main sources of the explicit beliefs and deliberate choices of System 2.
The automatic operations of System 1 generate surprisingly complex
patterns of ideas, but only the slower System 2 can construct thoughts in an
orderly series of steps. I also describe circumstances in which System 2
takes over, overruling the freewheeling impulses and associations of
System 1. You will be invited to think of the two systems as agents with
their individual abilities, limitations, and functions.
In rough order of complexity, here are some examples of the automatic
activities that are attributed to System 1:
Detect that one object is more distant than another.
Orient to the source of a sudden sound.
Complete the phrase “bread and…”
Make a “disgust face” when shown a horrible picture.
Detect hostility in a voice.
Answer to 2 + 2 = ?
Read words on large billboards.
Drive a car on an empty road.
Find a strong move in chess (if you are a chess master).
Understand simple sentences.
Recognize that a “meek and tidy soul with a passion for detail”
resembles an occupational stereotype.
All these mental events belong with the angry woman—they occur
automatically and require little or no effort. The capabilities of System 1
include innate skills that we share with other animals. We are born
prepared to perceive the world around us, recognize objects, orient
attention, avoid losses, and fear spiders. Other mental activities become
fast and automatic through prolonged practice. System 1 has learned
associations between ideas (the capital of France?); it has also learned
skills such as reading and understanding nuances of social situations.
Some skills, such as finding strong chess moves, are acquired only by
specialized experts. Others are widely shared. Detecting the similarity of a
personality sketch to an occupatiohein occupatnal stereotype requires
broad knowledge of the language and the culture, which most of us

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possess. The knowledge is stored in memory and accessed without
intention and without effort.
Several of the mental actions in the list are completely involuntary. You
cannot refrain from understanding simple sentences in your own language
or from orienting to a loud unexpected sound, nor can you prevent yourself
from knowing that 2 + 2 = 4 or from thinking of Paris when the capital of
France is mentioned. Other activities, such as chewing, are susceptible to
voluntary control but normally run on automatic pilot. The control of attention
is shared by the two systems. Orienting to a loud sound is normally an
involuntary operation of System 1, which immediately mobilizes the
voluntary attention of System 2. You may be able to resist turning toward
the source of a loud and offensive comment at a crowded party, but even if
your head does not move, your attention is initially directed to it, at least for
a while. However, attention can be moved away from an unwanted focus,
primarily by focusing intently on another target.
The highly diverse operations of System 2 have one feature in common:
they require attention and are disrupted when attention is drawn away.
Here are some examples:
Brace for the starter gun in a race.
Focus attention on the clowns in the circus.
Focus on the voice of a particular person in a crowded and noisy
room.
Look for a woman with white hair.
Search memory to identify a surprising sound.
Maintain a faster walking speed than is natural for you.
Monitor the appropriateness of your behavior in a social situation.
Count the occurrences of the letter 
a
in a page of text.
Tell someone your phone number.
Park in a narrow space (for most people except garage attendants).
Compare two washing machines for overall value.
Fill out a tax form.
Check the validity of a complex logical argument.
In all these situations you must pay attention, and you will perform less well,
or not at all, if you are not ready or if your attention is directed
inappropriately. System 2 has some ability to change the way System 1
works, by programming the normally automatic functions of attention and
memory. When waiting for a relative at a busy train station, for example,

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you can set yourself at will to look for a white-haired woman or a bearded
man, and thereby increase the likelihood of detecting your relative from a
distance. You can set your memory to search for capital cities that start
with 
N
or for French existentialist novels. And when you rent a car at
London’s Heathrow Airport, the attendant will probably remind you that “we
drive on the left side of the road over here.” In all these cases, you are
asked to do something that does not come naturally, and you will find that
the consistent maintenance of a set requires continuous exertion of at least
some effort.
The often-used phrase “pay attention” is apt: you dispose of a limited
budget of attention that you can allocate to activities, and if you try to
i>Cyou try tgo beyond your budget, you will fail. It is the mark of effortful
activities that they interfere with each other, which is why it is difficult or
impossible to conduct several at once. You could not compute the product
of 17 × 24 while making a left turn into dense traffic, and you certainly
should not try. You can do several things at once, but only if they are easy
and undemanding. You are probably safe carrying on a conversation with a
passenger while driving on an empty highway, and many parents have
discovered, perhaps with some guilt, that they can read a story to a child
while thinking of something else.
Everyone has some awareness of the limited capacity of attention, and
our social behavior makes allowances for these limitations. When the
driver of a car is overtaking a truck on a narrow road, for example, adult
passengers quite sensibly stop talking. They know that distracting the
driver is not a good idea, and they also suspect that he is temporarily deaf
and will not hear what they say.
Intense focusing on a task can make people effectively blind, even to
stimuli that normally attract attention. The most dramatic demonstration
was offered by Christopher Chabris and Daniel Simons in their book 
The
Invisible Gorilla
. They constructed a short film of two teams passing
basketballs, one team wearing white shirts, the other wearing black. The
viewers of the film are instructed to count the number of passes made by
the white team, ignoring the black players. This task is difficult and
completely absorbing. Halfway through the video, a woman wearing a
gorilla suit appears, crosses the court, thumps her chest, and moves on.
The gorilla is in view for 9 seconds. Many thousands of people have seen
the video, and about half of them do not notice anything unusual. It is the
counting task—and especially the instruction to ignore one of the teams—
that causes the blindness. No one who watches the video without that task
would miss the gorilla. Seeing and orienting are automatic functions of
System 1, but they depend on the allocation of some attention to the

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relevant stimulus. The authors note that the most remarkable observation
of their study is that people find its results very surprising. Indeed, the
viewers who fail to see the gorilla are initially sure that it was not there—
they cannot imagine missing such a striking event. The gorilla study
illustrates two important facts about our minds: we can be blind to the
obvious, and we are also blind to our blindness.